This invention relates to rangefinders; and more particularly relates to a novel and improved method and apparatus for determining the range or distance of an object which is particularly adaptable for use in rifle scopes and other powered scopes, such as, binoculars.
Various approaches have been taken in the design and construction of rangefinders to the end of simplifying both the method and apparatus for range finding as well as to provide a device which is compact, highly accurate and dependable in use. Mechanical ranging instruments from rifle scopes to electronic rangers are based on the trigonometric relationship between the known height of a distant object and the angle it presents to the viewer. Thus, when the viewer focuses on a distant object for the purpose of determining its range or distance, it is possible to make that determination in accordance with the formula ##EQU1## where h equals known height of the object and .crclbar. equals the Minutes of Angle (MOA) between imaginary lines extending from the viewer to the top and bottom of the object being viewed. In order to determine the actual or target height of the object, it is customary practice to employ a reticle scale on a see-through display with a predetermined spacing between elements or marks on the scale based on a spacing of 2.5 MOA between elements or marks. For example, assuming that ten marks on the display equal 4' in height at 100 yards, the spacing between adjacent marks equals 0/076.degree. C. or 2.5 MOA. Of course, for greater accuracy, the spacing between marks on the scale can be reduced. In any event, the target or object being viewed is lined up in the display such that the bottom of the target is at a reference line on the display and the marks on the scale will be arranged in ascending order from the reference line so that the user can match or determine which one of the selected marks is aligned with the upper edge of the object and which would represent its actual height above the reference line. Selection of that mark by the user when transmitted to a microprocessor is then placed in the formula together with the known height of the object.
In the past, efforts have been made to integrate all of the procedures necessary to calculate distance into a single optical package so that it is not necessary for the user to look away from the display or object sighted in carrying out the range finding operation.
Representative of approaches taken in the past are those disclosed in U.S. Pat. Nos. 4,787,739 to Gregory, 4,531,052 to Moore and 5,020,902 to Kits Van Heyningen et al. For example, in Van Heyningen, the digital display is transparent and positioned in the optical path such that the object can be viewed through the display, and the user inputs the actual or target height of the target object by controlling the number of bar segments shown on the display so that the uppermost bar segment which appears on the display is aligned with the upper edge of the target object, and the user may then enter that height by closing a switch to enter that reading into the microprocessor. Another switch is then closed to enter the known height of the object by incrementing another digital display until the value of the digit shown on the display is equal to the value of the digit for the known height. However, that known height value must be obtained by the user from a separate chart or by the user's own knowledge of actual height of the object. Then, by depressing or closing another switch to advance the microprocessor into the range mode, the necessary calculation is made to determine range based on the actual height and known height values entered, and the range is then displayed to the user. In the '052 patent to Moore, multiple images of the object are stored which are representative of the object at different distances from the observer and then compared with the object as viewed. In the '739 patent to Gregory, the multiple objects which are stored can have different sizes representative of the objects at different distances from the observer.
It is highly desirable to integrate a chart displaying known heights of different objects into the apparatus and in such a way that those known heights may be called up and presented on the same display as provided for viewing of the object so that the user can simultaneously view the magnified object and, through finger-operated switches, operate the display to select the known height from the chart displayed of known heights without refocusing the eyes or having to rely upon the user's memory for a wide range of different known heights for various objects to be viewed. Furthermore, it is also desirable to provide for novel and improved reticle scales and methods and means for displaying the actual or target height which are simple to operate and highly accurate.